Use of creams and ointments containing active ingredients are a popular means of dermal treatment of not only skin ailments but also for providing an alternative way of delivering drugs either locally or even systemically. Examples include creams for arthritis pain which contain Diclofenac or Ketorolac, creams for aching muscles which contain methyl salicylate and menthol, and creams containing hormones such as estrogens and testosterone for systemic delivery through skin and etc. Specialty creams ordered by physicians are easily prepared (compounded) by a pharmacist right in the pharmacy. However, such combinations of semi-solid materials and an active ingredient are often applied non-uniformly and in a manner that fails to regulate delivery of the active ingredient to the skin in a controlled manner. In addition, exposing the vehicle and active ingredient directly to the atmosphere tends to slow the diffusion of the active ingredient into the skin due to loss of moisture or evaporation of volatile penetration enhancers such as alcohol in the vehicle.
Transdermal drug delivery devices in the form of patches have been used to facilitate the delivery of active ingredients through the skin. There are generally two types of such patches. In the “reservoir” style patch, the active ingredient is disposed in a reservoir on the patch and is not mixed in with the adhesive. The reservoir is disposed on a backing to which a skin adhesive is applied. A membrane overlies the reservoir, and a release liner is placed over the membrane, adhesive, and reservoir. The membrane prevents the release liner from removing the active ingredient from the reservoir when the release liner is removed. However, the membrane also limits the rate of diffusion of the active ingredient into the skin.
In the “monolithic” or “drug-in-adhesive” style of patch, the adhesive and active ingredient are mixed together, possibly with other components such as plasticizers, excipients, and penetration enhancers. The combination of adhesive and active ingredient is applied to a backing, and there is no separate reservoir that includes the active ingredient. A release liner is typically provided over the combination of adhesive/active ingredient when the patch is being stored or transported for later use. Monolithic patches are only suitable for use with active ingredients that can be solubilized by suitable skin contact adhesives and in some cases require other components such as stabilizers to prevent precipitation of the drug from the drug-in-adhesive matrix. In addition, there is a variety of active ingredients for which the manufacture of pre-loaded transdermal drug delivery devices is not currently economically feasible. Thus, a need has arisen for a transdermal drug delivery device that addresses the foregoing issues.